Diesel engines
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Though not a PA28, our C182 SMA is great. We've had some alternator wiring problems (now fixed hopefully, and not really related to the type of fuel burnt).
But the aircraft flies further, faster, with more on board than the avgas original - and for a fraction of the cost (fuel only, £20/hour instead of £80+).
Fly safe, Sam.
But the aircraft flies further, faster, with more on board than the avgas original - and for a fraction of the cost (fuel only, £20/hour instead of £80+).
Fly safe, Sam.
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True. And I think the most important difference between the two is that car diesel is supposed to have lubricating properties, while Jet-A does not. So if you use Jet-A in an unconverted car diesel engine, things like fuel pumps may seize up rather quickly.
Another issue is that car diesel is less able to withstand low (<-15C) temperatures. So the fuel operating temperatures at which you are allowed to start and to take-off are a lot stricter with car diesel.
When we had the DA40 with the 1.7 Thielert, there was a whole POH supplement about using car diesel, temperature ranges and such. But since car diesel is essentially unobtainable airside, I never bothered to read that supplement in full.
Another issue is that car diesel is less able to withstand low (<-15C) temperatures. So the fuel operating temperatures at which you are allowed to start and to take-off are a lot stricter with car diesel.
When we had the DA40 with the 1.7 Thielert, there was a whole POH supplement about using car diesel, temperature ranges and such. But since car diesel is essentially unobtainable airside, I never bothered to read that supplement in full.
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The Operation manual states that if Diesel is used, the Aircraft is not allowed to be started if the temp is -5c or lower.
You're also only allowed to using Anti icing agents with JET A not with Diesel.
We sold 5 x PA28's to Bangladesh this year, and when I was there building them back up and running them they were on normal Diesel, you'd never know the difference even in flight, but the lesson of only using clean fuel can be an expensive one in termos of LP and HP pumps.
You're also only allowed to using Anti icing agents with JET A not with Diesel.
We sold 5 x PA28's to Bangladesh this year, and when I was there building them back up and running them they were on normal Diesel, you'd never know the difference even in flight, but the lesson of only using clean fuel can be an expensive one in termos of LP and HP pumps.
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I just checked the DA40 flight supplement which we had for the 1.7 Thielert, and the situation is even more complicated.
With diesel, or a blend of diesel and Jet-A (anything over 10% diesel would be considered a blend) the minimum engine starting temperature of the fuel is indeed -5C, but the minimum take-off temperature is +5C. So once you've got the engine started, you've got to wait for the fuel in the main tank to reach +5C. Furthermore, fuel transfer from aux to main is not guaranteed if the fuel in the aux tank is lower than +5C.
In contrast, the limit on Jet-A is -30C, both for starting and take-off.
The fuel is heated because the excess fuel in the common rail is led back to the main tank, via a coil in the aux tank. And the fuel is heated up in the common rail not just because of the ambient temperature in the engine compartment, but also because of the pressurization to ~400 bar.
With diesel, or a blend of diesel and Jet-A (anything over 10% diesel would be considered a blend) the minimum engine starting temperature of the fuel is indeed -5C, but the minimum take-off temperature is +5C. So once you've got the engine started, you've got to wait for the fuel in the main tank to reach +5C. Furthermore, fuel transfer from aux to main is not guaranteed if the fuel in the aux tank is lower than +5C.
In contrast, the limit on Jet-A is -30C, both for starting and take-off.
The fuel is heated because the excess fuel in the common rail is led back to the main tank, via a coil in the aux tank. And the fuel is heated up in the common rail not just because of the ambient temperature in the engine compartment, but also because of the pressurization to ~400 bar.
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Silvaire 1
Like a lot of people in this industry you are critical of a technology that you only have a passing knowlage of.
Most composite propellers are a wooden core with a carbon of glass re enforced plastic outer shell with a metal leading edge.
Damage to a metal prop is usually limited to blending the damage ( removal of metal) down to a manufactures limit.
Damage to composite blades is a more complicated issue but damage to a blade of a depth that would write off a metal prop is more than likely to be able to be repaired on a composite prop.
The composite Hartzell prop is a very different item being almost totaly carbon reenforced plastic, I am told with a metal spar. This is so new that I have no idea what the manufactures have mandated in the way of repaires but it looks like a very efficient areofoil and I am sure will out perform most other props.
Most composite propellers are a wooden core with a carbon of glass re enforced plastic outer shell with a metal leading edge.
Damage to a metal prop is usually limited to blending the damage ( removal of metal) down to a manufactures limit.
Damage to composite blades is a more complicated issue but damage to a blade of a depth that would write off a metal prop is more than likely to be able to be repaired on a composite prop.
The composite Hartzell prop is a very different item being almost totaly carbon reenforced plastic, I am told with a metal spar. This is so new that I have no idea what the manufactures have mandated in the way of repaires but it looks like a very efficient areofoil and I am sure will out perform most other props.
Silvaire 1 - Like a lot of people in this industry you are critical of a technology that you only have a passing knowlage of. [sic]
A close friend and colleague who I see at least weekly at his factory is the principal, designer, analyst and manufacturer of what are arguably the world's leading high end carbon fiber bladed propellers, sold in substantial volume for quite some years now. The blades FYI are 100% carbon fiber composite, very strong, with either hollow or foam core. Other than being produced with really clever manufacturing technology that he's developed over the last 20 years, the blades also have super-hard electro-formed nickel leading edges produced by a low cost proprietary method, fitting perfectly, and wrapping around the tip for maximum protection. These are a very good design, with good blade shape and excellent performance... but the blades still aren't as tolerant of abuse or abrasion as an aluminum prop. Damaged carbon fiber blades are not often repaired, they are generally replaced. Sometimes the manufacturer can replace the nickel leading edge, if the damage is limited to that part of the blade.
Of direct relevance to the diesel engine discussion, I also own and operate an MT 'composite' propeller that I inherited with my own aircraft, almost identical to those used with Thielert diesel engines, and relatively old fashioned in its construction. Mine was overhauled and reinstalled last month. It has a very thin layer of fiberglass over the wood, intended only as a weather shield, not as blade structure. The structure is entirely wood, retained with lag screws, but applicable to diesels because wood damps out torque pulsations well and thereby limits the resulting blade stress. The very thin layer of fiberglass is used because any thicker layer tends to delaminate - for structural reasons the glass layer needs to be very thin and very light, so thin you can see the grain of the wood through the fiberglass. The stainless leading edge MT uses is also rudimentary old-style technology, formed mechanically and much softer than a nickel leading edge. The net result in my opinion is a quite fragile propeller. If it survives any abuse that might be applied between overhaul cycles it really does require the 6 year overhaul period recommended by MT. A completely different world of fragility, complexity and maintenance when compared to the normal fixed pitch prop on a 172 or Cherokee, and also IMO much less durable than an aluminum CS propeller.
Perhaps that may be useful to those who would like to build a genuinely greater than passing knowledge of composite propellers, particularly as currently applied to diesel aircraft engines.
Take care.
Last edited by Silvaire1; 2nd Oct 2013 at 02:51.
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Silvaire1
That is all very interesting but your first post on the subject did sound just like the usual head in the sand critsisum of new Technoligy.
I find that following years in the maintenance business that we have substantially less MT prop blades written off at overhaul than we do metal blades, this can only be because blades are more damage tolerant in terms of overhaul limits.
The in service damage to metal and composite props seems to be much the same, mostly on the leading edge as you would expect but the leading edge non structural metal shield on the MT is more damage tolerant in the fact that damage to to won't start a fatigue crack as it can on a metal prop
I can only speak as I find on the aircraft we look after but the MT props are fitted to a diverse types ranging from Thielert powered PA28's & Daimonds to Extra 300 types so I do get to see props from a wide slice of this industry and would take a guess that the cost of ownership of an MT prop is likely to be on average 10-15% lower in terms of overhaul costs.
I find that following years in the maintenance business that we have substantially less MT prop blades written off at overhaul than we do metal blades, this can only be because blades are more damage tolerant in terms of overhaul limits.
The in service damage to metal and composite props seems to be much the same, mostly on the leading edge as you would expect but the leading edge non structural metal shield on the MT is more damage tolerant in the fact that damage to to won't start a fatigue crack as it can on a metal prop
I can only speak as I find on the aircraft we look after but the MT props are fitted to a diverse types ranging from Thielert powered PA28's & Daimonds to Extra 300 types so I do get to see props from a wide slice of this industry and would take a guess that the cost of ownership of an MT prop is likely to be on average 10-15% lower in terms of overhaul costs.
Last edited by A and C; 2nd Oct 2013 at 07:32.
Having flown a little over 70 hours in an SMA powered 182 so far, and experienced no fewer than three alternator failures of varying types, I can attest to the value of the mechanical back-up mode; given how often the electrical system fails, the aircraft would be frankly dangerous without it.
The mechanical back-up mode limits the power you can use, typically slowing one down by about 10 knots in cruise, and it also tends to cut the engine completely if power is reduced below about 1000 RPM (idle is 600ish). This will really screw you up on landing if you're not ready for it. Ultimately, it's far preferable to engine failure when your battery drains though.
The SMA is also very prone to over-heating in high ambient temperatures.
I'd love to fly behind the newer version of the SMA engine and see how things have been improved.
I've also flown behind the Thielert in both DA40 and Robin applications and had no issues there. Overall, I'm a big fan of diesels.
The mechanical back-up mode limits the power you can use, typically slowing one down by about 10 knots in cruise, and it also tends to cut the engine completely if power is reduced below about 1000 RPM (idle is 600ish). This will really screw you up on landing if you're not ready for it. Ultimately, it's far preferable to engine failure when your battery drains though.
The SMA is also very prone to over-heating in high ambient temperatures.
I'd love to fly behind the newer version of the SMA engine and see how things have been improved.
I've also flown behind the Thielert in both DA40 and Robin applications and had no issues there. Overall, I'm a big fan of diesels.
Last edited by Katamarino; 2nd Oct 2013 at 17:28.
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I have been following aero diesels for ages and I believe there are more in development than their are avgas engine companies at the moment.
Technically an externally scavenged two stoke is a better choice for a diesel,
more power pulses per rev and lower peek torque pulses. With 4 cyl 4 strokes, aka the SMA & Centurion the prop is driving the engine 30% of the time. So the prop is experiencing high torque reversals, not good, brute force engineering over common sense.
These are all 2 strokes
The nicest is the Zoche 8cyl twin row radial at 300hp for the weight of the unreliable IO360. Runs like a sowing machine. But I think it has turned into an EU grants scam.
The US Delta Hawk V4 200hp is looking very good not certified yet.
The Wilksch inverted 3/4 cyl is also very good.
There are many opposed piston units in development, nice low vibration designs. With some like the Ecomotors OPOC and the FairDiesel novel designs.
Diesels are coming but I hope the 2 strokes will win in the end, so much better.
Technically an externally scavenged two stoke is a better choice for a diesel,
more power pulses per rev and lower peek torque pulses. With 4 cyl 4 strokes, aka the SMA & Centurion the prop is driving the engine 30% of the time. So the prop is experiencing high torque reversals, not good, brute force engineering over common sense.
These are all 2 strokes
The nicest is the Zoche 8cyl twin row radial at 300hp for the weight of the unreliable IO360. Runs like a sowing machine. But I think it has turned into an EU grants scam.
The US Delta Hawk V4 200hp is looking very good not certified yet.
The Wilksch inverted 3/4 cyl is also very good.
There are many opposed piston units in development, nice low vibration designs. With some like the Ecomotors OPOC and the FairDiesel novel designs.
Diesels are coming but I hope the 2 strokes will win in the end, so much better.
@backpacker, surely the best way to preheat the fuel is to use a fuel heater/oil cooler like a CFM 56. Two jobs for the price of one. @yodi, can you provide a link to the bangladeshi operation?
regards
TDD
regards
TDD
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Last edited by YODI; 4th Oct 2013 at 09:11.
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Right now, I don't see the benefit of Diesel widespread. Yes, there are conversions, BUT these Centurion/Thielert/Technify have no longer TBO, they have TBR! So, no more overhaul, time's up is equal to get a new machine. Then you have the gear trouble with 300h between replacement and this itty nitty clutch, you have to have not to wreck the engine on stop. Further on, they don't run without electricity - I had so many Fadec failures, I cant count any longer.
I am keen on trying the SMA in the Cessna JT-A, as my feeling tend to see the gearless real-aviation Diesel still as an option. The automobile conversions in my eyes are not. Development cycles to press the last cent out of the buyers pocket in automotive is so short, it is not compatibel with the long cycles in aviation.
One remark to the EN590 issue - yes, there are engines out, that state compliance with EN590, BUT - BIG BUTT, this refers to the "old" EN590 only with pretty much defined max 5% RME addition - in secret they altered the EN590 to include up to 7% FAME instead of RME, which is unspecific fatty acids bio crap. This standard Diesel from tap is not compliant to aviation use.
I am keen on trying the SMA in the Cessna JT-A, as my feeling tend to see the gearless real-aviation Diesel still as an option. The automobile conversions in my eyes are not. Development cycles to press the last cent out of the buyers pocket in automotive is so short, it is not compatibel with the long cycles in aviation.
One remark to the EN590 issue - yes, there are engines out, that state compliance with EN590, BUT - BIG BUTT, this refers to the "old" EN590 only with pretty much defined max 5% RME addition - in secret they altered the EN590 to include up to 7% FAME instead of RME, which is unspecific fatty acids bio crap. This standard Diesel from tap is not compliant to aviation use.
As a diesel ignoramus I'd be very interested if someone could explain what it is that makes the engines that power current Le Mans winners so powerful and still light enough for racing.
I also wonder why the manufacturers of auto conversions all go for heavy steel four and six cylinder engines and not, say, the VW ten cylinder aluminium engine. If I read the advertising right it puts out 300 hp. at about 3,500 revs. If it was derated to 200 hp it would be right in its best torque range and might not even need a gearbox.
Granted it is complicated, (four stroke, twin turbo etc,) but then twelve cylinder 27 litre twin supercharger engines were reliable enough just after WW11, surely we could use a ten cylinder engine today and with those small pots and small crank offset the vibration might be less too.
I also wonder why the manufacturers of auto conversions all go for heavy steel four and six cylinder engines and not, say, the VW ten cylinder aluminium engine. If I read the advertising right it puts out 300 hp. at about 3,500 revs. If it was derated to 200 hp it would be right in its best torque range and might not even need a gearbox.
Granted it is complicated, (four stroke, twin turbo etc,) but then twelve cylinder 27 litre twin supercharger engines were reliable enough just after WW11, surely we could use a ten cylinder engine today and with those small pots and small crank offset the vibration might be less too.
Last edited by ChrisVJ; 21st Jun 2014 at 23:47. Reason: Diesel ignoramus might learn to spell diesel
Reading the latest Pilot mag it would give the impression that with the newer breed of diesels there is indeed a place for them on light aircraft.
My main concern is not so much the technical side of things as all or most of these will undoubtedly be rectified at some stage. My worry is what our taxes loving government will do to the price of "aircraft" diesel fuel and Jet fuel when diesel powered aircraft are in the ascent (pun intended).
As has happened to the automotive side of things and yes I do understand that modern diesel fuels are more refined but not to the extent where they are dearer than petrol.
My main concern is not so much the technical side of things as all or most of these will undoubtedly be rectified at some stage. My worry is what our taxes loving government will do to the price of "aircraft" diesel fuel and Jet fuel when diesel powered aircraft are in the ascent (pun intended).
As has happened to the automotive side of things and yes I do understand that modern diesel fuels are more refined but not to the extent where they are dearer than petrol.
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The diesels at LeMans are there because of the fuel formula, demanding much higher efficiency than the petrol classes.
Unfortunately the longevity of those engines is measured in a race (especially if it lasts 24hrs!).
If you read any of the autobiographies of post war commercial pilots you will find numerous engine failures. That is why we still have the whole multi-engine mindset in aircraft. I used to know a chap who flew Super Constellations, 32 cylinders, turbo and super charged engines. He said it was almost unusual to make an Atlantic crossing and have 4 fully functional engines at the end, they were nearly always nursing one!
Diesels will come but it will need some serious money and good engineering. To date neither of those have really happened.
The Wilksh cannot really be built in serious numbers due to the cost/complexity of its gudgeon pin arrangement.
The Thielert and other conversions offer no real advantage and as noted above have a TBR - which is really a killer in terms of value.
Deltahawk - dunno I've been watching the website for years, will they ever produce an engine?
SMA? massively expensive and it seems still having issues.
Patience is required it seems!
Unfortunately the longevity of those engines is measured in a race (especially if it lasts 24hrs!).
If you read any of the autobiographies of post war commercial pilots you will find numerous engine failures. That is why we still have the whole multi-engine mindset in aircraft. I used to know a chap who flew Super Constellations, 32 cylinders, turbo and super charged engines. He said it was almost unusual to make an Atlantic crossing and have 4 fully functional engines at the end, they were nearly always nursing one!
Diesels will come but it will need some serious money and good engineering. To date neither of those have really happened.
The Wilksh cannot really be built in serious numbers due to the cost/complexity of its gudgeon pin arrangement.
The Thielert and other conversions offer no real advantage and as noted above have a TBR - which is really a killer in terms of value.
Deltahawk - dunno I've been watching the website for years, will they ever produce an engine?
SMA? massively expensive and it seems still having issues.
Patience is required it seems!
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A question.
If props on diesels are subject to vibration and tourque reversal problems why can you no add a cush drive? By this i mean the rubber shock absorber arrangement used on motorbike rear wheels to damp the pulses from single or twin cylinder engines.
If props on diesels are subject to vibration and tourque reversal problems why can you no add a cush drive? By this i mean the rubber shock absorber arrangement used on motorbike rear wheels to damp the pulses from single or twin cylinder engines.